3.9 Enthalpy Change Flashcards
Enthalpy Definition
A measure of the heat energy in a chemical system.
Conservation of energy
Energy cannot be created or destroyed.
Enthalpy change (General)
Products - Reactants
Exothermic Reaction
Energy transfer from the system to the surroundings. Change of energy is negative.
Endothermic Reaction
Energy transfer from the surroundings to the system. Change of energy is positive.
Activation energy
The minimum energy required for a reaction to take place.
Standard conditions
100 kPa, 298 K, 1 mol dm^-3
Standard enthalpy Change of a Reaction.
The enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under STP, with all
reactants and products in their standard states.
Standard Enthalpy Change of Formation.
The enthalpy change that takes place when one mole of a compound is formed from its elements under STP.
Standard Enthalpy Change of Combustion
The enthalpy change that takes place when one mole of a substance reacts completely with oxygen under STP.
Standard Enthalpy Change of Neutralisation
The energy change that accompanies the reaction of an acid by a base to form 1 mole of H2O under STP.
The equation for the energy change of surroundings
q = masscchange in temperature.
Average Bond Enthalpies
The energy required to break one mole of a specific type of bond in a gaseous molecule.
Limitations of Average Bond Enthalpies
Enthalpy changes are different in different chemical situations.
Bond Breaking is …
Endothermic
